Ultrasonic surgical tool capable of vibrating in plural modes and a drive system that induces non-linear vibrations in the tool tip

ABSTRACT

An ultrasonic surgical tool system with a tip capable of simultaneously vibrating in plural modes. The system includes a console capable of supplying a drive signal to the tip that includes plural components. Each component has a frequency characteristic that is based in part on the equivalent of current through the mechanical components of the tip. The frequency components are different from each other. Based on the application of drive signal the tip undergoes non-linear vibrations.

FIELD OF THE INVENTION

This application is generally related to an ultrasonically drivensurgical handpiece. More particularly, this invention relates to anultrasonically driven handpiece that has plural modes of vibration and amethod of driving the handpiece so the tip head undergoes non-linearvibrations.

BACKGROUND OF THE INVENTION

Ultrasonic surgical instruments are useful surgical instruments forperforming certain medical and surgical procedures. Generally, anultrasonic surgical tool includes a handpiece that contains at least onepiezoelectric driver. A tip is mechanically coupled to the driver andextends forward from the housing or shell in which the driver isdisposed. The tip has a head. The head is provided with features, oftenteeth, dimensioned to accomplish a specific medical/surgical task. Anultrasonic tool system also includes a control console. The controlconsole supplies an AC drive signal to the driver. Upon the applicationof the drive signal to the driver, the driver cyclically expands andcontracts. The expansion/contraction of the driver induces a likemovement in the tip and more, particularly, the head of the tip. Whenthe tip so moves, the tip is considered to be vibrating. The vibratinghead of the tip is applied against tissue to perform a specific surgicalor medical task. For example, some tip heads are applied against hardtissue. One form of hard tissue is bone. When this type of tip head isvibrated, the back and forth vibrations of the tip teeth, saw, remove,the adjacent hard tissue. Still other tip heads are designed to beplaced against soft tissue. Some ultrasonic tools also remove tissue byinducing cavitation in the tissue and surrounding fluid. Cavitationoccurs as a result of the tip head moving back and forth. Specifically,as a result of these vibrations, small voids, cavities, form in thetissue and surrounding fluid. These cavities are small zones ofextremely low pressure. A pressure differential develops between thecells forming the tissue and these cavities. Owing to the relativelylarge magnitude of this pressure differential, the cell walls burst. Thebursting of these cell walls, removes, ablates, the cells forming thetissue.

The head of an ultrasonic tip is often relatively small. Some heads havediameters of less than 1.0 cm. An ultrasonic tool essentially onlyremoves the tissue adjacent to where the head is applied. Owing to therelative small surface area of their heads, ultrasonic handpieces haveproven to be useful tools for precisely removing both hard and softtissue.

Most tips are designed so that when the drive signal is applied, the tiphead vibrates in a single mode. Here the vibration mode is understood tobe the path of travel along which the tip head travels. The majority oftips are designed to vibrate linearly. This means the heads move backand forth along an axis that is essentially in line with theproximal-to-distal longitudinal axis along the tip. Some tips aredesigned so that their heads, when vibrated, engage in a torsional orrotation vibration. This means that that head, when excited intovibration, rotates around the tip longitudinal axis. Still other tipsare designed to flex. This means that when the tip is excited, thelongitudinal axis of the tip bends back and forth. The tip head moveswith the bending, the flexing, of the tip.

Problems can arise when a tip head only vibrates longitudinally. This isbecause this type of tip head movement frequently induces cavitation inthe tissue along the tip shaft. This can be a problem when the tip isused to remove hard tissue, bone, in close proximity to soft tissue thatshould not be subjected to removal. Types of soft tissue that should notbe removed included both blood vessels and tissue that is part of thenervous system. The problem occurs because the cavitation can result inthe unwanted removal of this soft tissue.

Tips are now available that reduce this unwanted cavitation. These tipsare designed to vibrate in two modes. The tip vibrates longitudinally.The tip also vibrates torsionally, around the longitudinal axis of thetip shaft. One such tip is the Long Micro Claw tip available from theApplicant, Stryker Corporation, of Kalamazoo, Mich. The structure ofthis tip is disclosed in U.S. Pat. No. 6,955,680, COUPLING VIBRATIONULTRASONIC HAND PIECE, the contents of which is explicitly incorporatedby reference.

When a drive signal is applied to a tip capable of vibrations indifferent modes, the tip head undergoes a movement that is the sum ofthe vibratory displacements. The head of a tip capable of simultaneouslongitudinal and torsional vibrations when driven, simultaneouslyoscillates longitudinally and rotationally. FIG. 1 depicts thismovements at a point on the tip head. As a result of these simultaneousvibrations, a point on the tip head moves back and forth along a sectionof helix. This movement is thus proximally and distally along thelongitudinal axis of the head and rotationally around the longitudinalaxis.

An advantage of so vibrating the tip is that the extent the tip shaftvibrates longitudinally is reduced. This results in a like reduction inthe unwanted removal of tissue adjacent the shaft.

While the above ultrasonic tool system is useful, it is not without somedisadvantages. One disadvantage is that, for this system to function,the two modes of vibration have to occur at the same frequency. Thisrequires the tip to be especially designed to vibrate in this mode. Thisconstrains the tips to certain sizes and shapes. This can make itdifficult to provide tips able to be applied to sites in order toperform certain tissue removal procedures. Further, having to design atip to this requirement can make the tip relatively expensive toproduce.

Further, when a tip head undergoes this type of movement, an individualtooth on the tip head moves back and forth on a section of helix. Thismovement is over a track of typically less than 300 microns in length.In practice the movement of a single tooth is along a line that isdiagonal to the longitudinal axis of the tip shaft. When an individualtooth cuts into bone, the tooth forms a groove that is diagonal to thisaxis. The back and forth motion of the tooth in a groove places aresistance against the tip that inhibits the motion of the head otherthan along the directions of the groove. This resistance can beappreciable because each tooth travels in its own groove. This inhibitsthe ability of the practitioner to steer, position, the tip in thedesired direction.

Moreover, as a result of any cutting operation, the cut material formsdebris in the vicinity of the tool performing the cutting. This appliesto situations when an ultrasonic surgical tool is used to remove tissue.When the teeth of an ultrasonic surgical tool move back and forth in alinear path of travel the debris tend to accumulate between the teeth.The accumulation of these debris adversely affects the ability of theteeth to dig in and remove tissue.

SUMMARY OF THE INVENTION

This invention is related to a new and useful ultrasonic surgical toolsystem. The system of this invention includes a tip that, when vibrated,vibrates in plural modes. The system of this invention further includesa drive system that applies a drive signal to the tip that causes thetip head to, when vibrated, move along a path of travel that isnon-linear.

The system of this invention typically includes a drive system capableof providing a cumulative drive signal. This cumulative drive signal isthe sum of plural distinct components. Typically the drive signal hasone component for each vibration mode of the tip. In many versions ofthe invention, each component has a frequency characteristic. Thefrequency characteristic is a frequency that is at or near a targetfrequency of a particular vibrational mode of the tip. Here a vibrationmode may be the vibration of the tip in a single plane, longitudinal,torsional or flexural. Typically, the frequency characteristics of thedifferent vibration modes are different from each other. Alternatively,the vibration mode may be for a vibration that occurs simultaneously intwo or more of planes. Here the target frequency is a frequencysomewhere between and including the resonant and anti-resonantfrequencies of the tip within the range of frequencies for the specificrange of frequencies in which the tip is to vibrate.

It is a further feature of this invention to change the characteristics,the frequency and voltage, of each component of the drive signal. Thesecharacteristics are changed because, during use of the ultrasonic tool,the tip head is subjected to resistance, mechanical loading. Thisloading changes the equivalent of impedance of the mechanical componentof the handpiece. The change in this characteristic of the handpiecechanges how the tip head moves, vibrates, in response to the applicationof the drive signal. To ensure that the tip head engages in the movementdesired by the practitioner, the system of this invention adjusts thedrive signal. This drive signal adjustment is performed by adjusting thecharacteristics of the components of the drive signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the claims. The aboveand other features and benefits of the invention are further understoodfrom the following Detailed Description taken in conjunction with theaccompanying drawings in which:

FIG. 1 depicts the vibratory movement of a tip head when actuated usinga prior art system;

FIG. 2 depicts the basic components of an ultrasonic tool system thatincludes the features of this invention;

FIG. 3 is a diagrammatic and exploded depiction of the mechanicalcomponents of the tool, the handpiece, tip and sleeve of the system;

FIG. 4 is a block diagram depicting the electrical components of thehandpiece and tip and how these components are connected to the controlconsole;

FIG. 5 depicts types of data stored in the memory internal to thehandpiece;

FIG. 6 depicts types of data stored in the memory integral with the tooltip;

FIG. 7 is a block diagram of the electrical components of the controlconsole and handpiece components of the system of this invention;

FIG. 8 depicts the waveform of the drive signal applied to the handpieceaccording to the system of this invention;

FIGS. 9A and 9B are representations of current flow through thehandpiece and the impedances of the different components of thehandpiece;

FIGS. 10A-10D, when assembled together, form a flow chart of theoperation of the system of this invention; and

FIG. 11 represents the movement of a single point on the head ofultrasonic tip when the tip is actuated according to this invention.

DETAILED DESCRIPTION I. System Overview and Hardware

An ultrasonic tool system 30 that includes the features of thisinvention is now generally described by reference to FIGS. 2 and 3.System 30 includes a handpiece 32. A tip 142 is attached to and extendsdistally forward from the handpiece 32. (“Distal” is understood to meanaway from the practitioner, towards the site to which the handpiece isapplied. “Proximal” is understood to mean towards the practitionerholding the handpiece, away from the site to which the handpiece isapplied.) Tip 142 is the component of system 30 that is applied totissue to perform the desired medical/surgical procedure. System 30 alsoincludes a control console 240. Control console 240 sources a drivesignal that is applied to the handpiece 32. In response to applicationof the drive signal, handpiece 32 causes tip 142 to vibrate.

Handpiece 32 includes a body or shell 34, see only in FIG. 2. From FIGS.3 and 4 it can be seen that one or more vibrating piezoelectric drivers36 (four shown) are disposed inside the shell 34. Each driver 36 isformed from material that, when a current is applied to the driver,undergoes a momentary expansion or contraction. Theseexpansions/contractions are on the longitudinal axis of a driver 36, theaxis that extends between the proximally and distally directed faces ofthe driver. A pair of leads 38 extends away from each driver 36. Leads38 are attached to the opposed proximally and distally directed faces ofthe drivers. Many, but not all, handpieces 32 include drivers 36 thatare disc shaped. Drivers 36 are arranged end to end in a stack. Leads 38are the components of system 30 over which the drive signal is appliedto the drivers 36. Insulating discs 40, one shown, are disposed betweenadjacent drivers. In FIG. 2, drivers 36 and the insulating disc 40 areshown spaced apart from each other. This is for ease of illustrating thecomponents. In practice drivers 36 and insulating discs 40 tightly abut.

A post 44 extends longitudinally through the drivers 36, leads 38 andinsulting discs. The post 44 extends through the drivers 36, leads 38,and insulating discs 40 and along the collinear longitudinal axes ofthese components. Not seen are through bores internal to the drivers 36,leads 38 and insulating discs through which the post 44 extends. Post 44projects outwardly of both the most proximally located driver 36 and themost distally located driver.

A proximal end mass 46 is located adjacent and abuts the proximallydirected face of the most proximally located driver 36. Mass 46 isattached to the proximal end section of post 44. If post 44 is threaded,mass 36 may be a nut.

A horn 48, seen only in FIG. 3, extends forward from the distallydirected face of the most distally located driver 36. Horn 48 has a basewith a diameter approximately equal to the diameter of the drivers 36.Extending distally forward from the drivers 36, the diameter of the horn48 decreases. The exposed distal end section of post 44 is affixed tothe horn 48. In many versions of the invention, post 44 and horn 48 area single piece unit. Handpiece 32 is constructed so that the stack ofdrivers 36 and insulating discs is compressed between proximal mass 36and horn 48.

Also disposed in handpiece shell 34 is a handpiece memory 56. Memory 56contains data used to regulate the operation of the handpiece 32 and tip142. Memory 56 may take the form of an EPROM, an EEPROM or an RFID tag.The structure of the memory is not part of the invention. For purposesof illustration handpiece memory 56 is an RFID tag. A coil 54 is shownconnected to memory 56. Coil 54 is the component associated with thehandpiece over which the control console 240 reads from and writes tothe handpiece memory 56.

FIG. 5 illustrates types of data stored in the handpiece memory 56.These data, as represented by field 62, include data identifying thehandpiece 32. These data are useful for verifying that the console 240is able to apply a drive signal to the handpiece. Data in field 62 mayalso indicate the type of information regarding the handpiece that ispresented on the console display 278. Other data in the handpiece memory56 are used to regulate the sourcing of drive signals to the drivers 36.While the use of these data are discussed below, the types of data arenow described. Field 64 contains data indicating the capacitance C_(O),the capacitance of the stack of drivers 36. Driver capacitance can bedetermined by analysis during the process of assembling the handpiece34. Often the sum of the capacitance of the drivers is between 500 to5000 pF. Data regarding the maximum current that should be applied tothe handpiece 36, current i_(S) ^(MAX), are contained in a field 66.Current is i_(S) ^(MAX) is often less than 1 Amp peak and more often 0.5Amp peak or smaller. Field 68 contains data indicating maximumequivalent of current, i_(M) ^(MAX), that should flow through the belowdiscussed mechanical components of the handpiece. Current i_(M) ^(MAX)is typically 0.25 Amps peak or less. The maximum potential of the drivesignal, voltage V_(S) ^(MAX), are stored in field 70. Voltage V_(S)^(MAX) is often 1500 Volts AC peak.

Also stored in handpiece memory 56 are data indicating the minimum andmaximum frequencies of the drive signal that should be applied tohandpiece 32. The minimum frequency, stored in field 72, is typicallythe minimum frequency of the drive signal that can be sourced by thecontrol console. The maximum frequency of the drive signal, stored infield 74, is typically between 5 kHz and 40 kHz Hz greater than theminimum frequency.

Field 76 contains coefficients for filtering the control signals outputby controller 96. PID control loops are used to establish the finallevels for each of these signals. Field 76 contains the coefficients foreach of these control loops. It should be understood that the data infields 62, 66, 68, 70, 72, 74 and 76, like the data in field 64, arestored in the handpiece memory 56 as part of the process of assemblingthe handpiece.

Handpiece memory 56 also contains field 78 as a use history field.Control console 240, during use of the handpiece 32, writes data intofield 128 so as to provide a log of the operation of the handpiece.

Returning to FIG. 4, it can be seen that also shown internal to thehandpiece 32 are two conductors 132. Conductors 132 extend from coil 54to the distal end of the handpiece. The conductors 132 are connected toa second coil, coil 134, also disposed in the handpiece 32.

Tip 142 extends forward from the handpiece horn 48. The tip 142 has agenerally cylindrical shaft 144. In some, but not all versions of theinvention, shaft 144 has plural sections each with a different crosssectional diameter. In the illustrated version of the invention, tipshaft 144 has a proximal section 146. Shaft proximal section 146 isformed with coupling features designed to facilitate the removablecoupling of the tip to handpiece 32. In one version of the invention,the handpiece coupling feature is a boss 49 that extends forward fromhorn 48. The outer surface of the boss 49 is formed with threading (notillustrated). The tip coupling feature is a closed end bore 145 thatextends inwardly from the proximal end of the shaft 144 partiallythrough the shaft proximal section 145. Bore 145 is provided withthreading (not illustrated) designed to engage the threaded bossintegral with the handpiece horn 48.

In the depicted versions of the invention, shaft 144 has a middlesection 150 that extends forward from the shaft proximal section 146.Middle section 150 has a diameter less than that of the proximal section146. The depicted shaft 144 has a distal section 156. Shaft distalsection 156 has a diameter less than that of the middle section 150.

A head 158 is the most distal portion of tip 142. Head 158 is locatedimmediately forward of the shaft proximal section 156. Head 158 issometimes formed with teeth or flutes (not illustrated). Tip head 158 isthe portion of system 30 pressed against tissue to perform a desiredprocedure. The teeth or flutes are designed so that when the head 158moves, the teeth or flute bear against tissue. As a consequence of themovement of the head, the teeth or flutes remove tissue. The geometry ofthe tip teeth or flutes is not part of the present invention.

Handpiece 32 is generally designed so that the back and forth movementof the drivers induce a like vibrating motion in the tip 142. These arelongitudinal vibrations in that the motion is back and forth along thelongitudinal axis of the tip and, more particularly, the shaft. A tip ofthis invention is further provided with features that convert theproximal to distal vibratory motion applied to the proximal end of theshaft into at least two different types of vibratory motion. In thedepicted tip 142 these features are helical grooves 152 that extendinwardly from the outer surface of shaft middle section 150. Owing tothe presence of grooves 152, a fraction of the longitudinal motionapplied to the shaft proximal section into motion that causes thesections of the tip forward of the grooves to, in addition to vibratinglongitudinally, vibrate rotationally. Rotational vibration is understoodto mean the vibration of the shaft and tip in an arc that extends aroundthe longitudinal axis of the shaft 144.

The tip 142 integrated into the system 30 of this invention is furtherdesigned so that the resonant frequencies of the vibrational modes aredifferent. Often these resonant frequencies are spaced between 200 and2000 Hz from each other.

A sleeve 170 is disposed around tip shaft 144. Sleeve 170 is formed ofplastic. The proximal end the sleeve is formed with features thatfacilitate the releasable coupling of the sleeve to the distal end ofthe handpiece horn 48. The components forming system 30 are formed sothat sleeve is spaced radially away from tip shaft 144 andlongitudinally away from tip head 160. More specifically the componentsare dimensioned so that during the normal vibration of the tip, the tipdoes not abut the sleeve.

While not part of the present invention, it can be seen that sleeve 170is often formed with a fitting 172. Fitting 172 is formed to receive anirrigation line. During use of system 30, irrigating fluid is oftenflowed into the sleeve 170. The fluid flows around through the gapbetween the tip 142 and the sleeve 170 and out the open distal end ofthe sleeve. Handpiece post 44 and the tip 142 are formed with contiguousbores (bores not illustrated). During a procedure, suction is drawnthrough these bores. The suction draws from the site to which tip head158 is applied the irrigating fluid as well as debris formed by theprocedure that are entrained in the fluid. The suction also draws tissuetowards the tip head 158. This drawing of the tissue towards the tiphead 158 enhances the cutting of the tissue by the tip head.

Disposed inside the sleeve is a tip memory 184, seen as a dashedrectangle in FIG. 3. Memory 184 is referred to as the tip memorybecause, even though the memory is disposed in sleeve 170 the memory isused to control the operation of the tip 142. Further, tip 142 andsleeve 170 are typically distributed together as a single package. Tip142 is typically initially first coupled to the handpiece 32. After thetip 142 is in place, the sleeve 170 is fitted to the handpiece. Tipmemory 184 is typically the same type of memory has handpiece memory 56.Accordingly, in the illustrated version of the invention, tip memory 184is an RFID tag. A coil 182, seen only in FIG. 4, embedded in sleeve 170is connected to the input pins of the tip memory 172. The componentsforming system 30 are constructed so that when the sleeve 170 is fittedto the handpiece 32, handpiece coil 134 and coil 182 are able to engagein inductive signal exchange.

FIG. 6 depicts the type of data contained in tip memory 184. Asrepresented by field 188, these data include a tip identification field.The data in field 188 identifies the tip and is analogous to the dataidentifying the handpiece in handpiece memory handpiece identificationfield 112. In field 190 data are stored indicating the maximumequivalent of current, i_(M) ^(MAXΣ), that should go through themechanical components of the handpiece. This concept is explained below.Field 191 stores data indicating a maximum potential V_(S) ^(MAX1) forthe first component of the drive signal. In a field 192 data are storedindicating the maximum equivalent of current, i_(M) ^(MAX1) that shouldgo through the mechanical components at a first one of components of thedrive signal. Field 193 stores data indicating a maximum potential V_(S)^(MAX2) for the second component of the drive signal. Field 194 storesdata indicating the maximum equivalent of current, V_(S) ^(MAX2), thatshould go through the mechanical components at a second one of thecomponents of the drive signal. Field 196 contains data defining theminimum frequency of the first component of the drive signal. Field 198contains data defining the maximum frequency of the first component ofthe drive signal. Field 202 contains data defining a first targetfrequency, ω^(TRGT1), for the first component of the drive signal. Field204 contains a virtual impedance coefficient, m₁, used in associatedwith the target frequency for the first component of the drive signal.

Field 206 contains data defining the minimum frequency of the secondcomponent of the drive signal. Field 208 contains data defining themaximum frequency of the second component of the drive signal. Field 210contains data defining a target frequency, ω_(TRGT2), for the secondcomponent of the drive signal. Field 212 contains a virtual impedancecoefficient, m₂, used in associated with the target frequency for thesecond component of the drive signal.

A PID coefficient field 216 contains filtering coefficients for thecontrol signals that for the tip may be more specific than the data inhandpiece memory PID coefficient field 76. Tip memory 184 also containsa tip use history field 218. During operation of system 30, the controlconsole 240 writes data to field 218 regarding use of the tip 142

Control console 240, now described with respect to FIGS. 2, 4 and 7,supplies the drive signal to handpiece 32 that results in the vibrationof tip 142. These components include a power supply 242. Power supply242 outputs a constant voltage signal typically between 1 and 250 VDC.In many versions of the invention, the maximum potential of the voltageoutput by power supply 242 is 150 VDC or less. The voltage produced bypower supply 242 is applied to an variable gain amplifier 244. A controlsignal, specifically a WAVEFORM_SET (W_S) signal, is applied toamplifier 244. The WAVEFORM_SET signal establishes the gain of thesignal produced by the amplifier. In many versions of the invention,amplifier 244 is a variable gain Class A amplifier capable of, inresponse to the WAVEFORM_SET signal, outputting an AC signal. Moreparticularly, amplifier 244 is capable of outputting a signal with afrequency of between 10 kHz and 100 kHz. Often the signal has a minimumfrequency of 20 kHz.

The output signal from amplifier 244 is applied to the primary winding254 of a transformer 248, also part of the control console 240. Thevoltage present across the secondary winding 258 of the transformer 248is the drive signal applied to the handpiece drivers 36. This voltage istypically a maximum of 1500 volts AC peak. The drive signal is appliedin parallel across the drivers 36.

Transformer 248 includes a tickler coil 256. The voltage present acrosstickler coil 256 is applied to a voltage measuring circuit 262. Based onthe signal across tickler coil 256, circuit 262 produces a signalrepresentative of the potential and phase of voltage V_(S), the voltageof the drive signal applied to the handpiece 32. A coil 264, alsodisposed in control console 72, is located in close proximity to one ofthe conductors that extends from the transformer secondary winding 258.The signal across coil 264 is applied to a current measuring circuit266. Circuit 266 produces a signal representative of the magnitude andphase of current i_(S), the current of the drive signal through thehandpiece.

The drive signal present across transformer secondary winding 258 ispresent at two conductive contacts 266 attached to a socket integralwith the control console (socket not illustrated).

The drive signal is applied to the handpiece drivers by a cable 230 seenonly in FIG. 1. In many constructions of system 30, handpiece 30 andcable 230 are a single unit. Cable 230 is connected to the controlconsole socket in which contacts 266 are located.

In versions of the invention wherein the handpiece 32 and cable 230 area single unit, handpiece coil 54 is disposed in the plug integral withthe cable. Disposed in the console socket is a complementary coil 268.The components forming the system are configured so that when the plugintegral with cable 230 is seated in the handpiece socket, coils 54 and268 are able to inductively exchange signals.

The signals representative of the drive signal voltage V_(S) and currenti_(S) are sourced to the handpiece drivers 36 are applied to a processor276 also internal to the control console 240. Control console 240 alsoincludes a memory reader 272. Memory reader 272 is connected at one endto console coil 268 and at an opposed end to processor 276. The memoryreader 272 converts the signals present across the coil 268 into datasignals processor 272 is able to read. Memory reader 272 also, inresponse to signals output by the processor 272, output signals acrosscoil 268 that cause the coil to output signals that result in thewriting of data to the handpiece memory 56 and tip memory 184. Thestructure of memory reader 268 complements the handpiece memory 102.Thus, memory reader can be: an assembly capable of reading data in aEPROM or EEPROM or an assembly capable of interrogating and reading datafrom an RFID tag.

Processor 272 generates the WAVEFORM_SET signal that is applied toamplifier 244. The processor 276 thus sets the characteristics of thedrive signal output by the control console 240 and applied to thehandpiece 32. The characteristics of the drive signal set by processor276 are the voltage and frequency of the drive signal. Processor 276determines these characteristics as a function of the characteristics ofthe handpiece 32 and the characteristics of the tip 134. Processor 96also determines the drive signal as a function of the acquiredmeasurements of voltage V_(s) and current i_(s).

A display 278 is built into control console 240. The image on display278 is shown as being generated by processor 276. Information depictedon display 278 includes: information identifying the handpiece 32 andthe tip; and information describing characteristics of the operatingstate of the system. Display 278 is often a touch screen display.Processor 272 causes images of buttons to be presented on the display.By depressing the buttons, the practitioner is able to set what he/shedesires as specific operating characteristics of the system 30.

In addition to the buttons presented on the display 278, there istypically at least one on on/off switch associated with the controlconsole. In FIGS. 2 and 7, this on/off switch is represented by afootswitch 280.

Footswitch 280 is configured to generate a signal that varies with theextent to which the switch is depressed. The signal is sourced toprocessor 280. Based on the state of the signal sourced by thefootswitch 280, processor 276 regulates the generation of the drivesignal so as to control both whether or not the tip vibrates and themagnitude of the tip head vibrations.

II. Fundamentals of Operation

System 30 of this invention is designed so that the control console 240outputs a drive signal that results in the tip head 158 moving along apath of travel that can be considered non-linear. For the purposes ofthis invention, a non-linear path of travel is a path of travel suchthat when the tip head 158 oscillates back and forth, the movement of asingle point of the head is along two different sets of points in space.When the tip head engages in outbound phase of a single cycle ofmovement, relative to a starting point, the tip head travels along afirst set of the points. When the tip head engages in an inbound phaseof the same cycle to return to the starting point, the tip head travelsalong a second set of points that is separate from the first set ofpoints. Further, the set of points along which the tip head pointtravels during a first complete oscillatory cycle may be different fromthe set of points along which the tip head in the next oscillatorycycle. It should be understood that during an oscillatory cycle the setof points along which the tip head travels may not be in a single plane.The set of points may be in plural planes. Stated another way, the setof points may rotate around one or more axes.

FIG. 8 depicts the waveform of the drive signal control console 240outputs to the handpiece drivers 36 to induce the above-describedmovement of the tip head 158. The drive signal is the sum of two ACsignals, referred to now as drive signal components. Each drive signalcomponent has its own frequency and its own potential. Typically, thefrequencies of these different components are different. Also, often,the potentials of the different components of the drive signal aredifferent from each other.

It is a further feature of many versions of this invention eachcomponent of the drive signal is at a frequency that is at or near atarget frequency of a particular vibrational mode of the tip. System 30may be configured so that a vibrational mode is the vibration of the tipin a single plane, longitudinal, torsional or flexural. Here it isunderstood that vibration in the longitudinal plane is reciprocalmovement along the longitudinal axis of the tip 142. Vibration in thetorsional plane is understood to be rotational reciprocal movement ofthe tip head 158 in a plane perpendicular to the longitudinal axis ofthe tip head. Flexural movement is reciprocal movement of the tip headin a plane in which the longitudinal axis of the tip is disposed.Flexural movement is thus the bending of the tip around the shaft 144.This flexural movement can occur in any direction in the 360° around theshaft. Alternatively, the vibrational mode of the tip 42 may be avibrational mode may be a vibration that is simultaneous reciprocalmovement of the tip in two planes. For example, one vibrational mode maybe longitudinal and torsional such that the motion is along a first linethat is intersects the longitudinal axis of the tip shaft. The secondmode may be a second combined longitudinal and torsional motion that isalong a line. The difference between these two vibratory modes is thatthe second mode vibrations are along a line that is separate from theline of vibrations of the first mode.

The “target frequency” for a tip vibrational mode according to thisinvention is a frequency within the range of frequencies the tip 142 issupposed to vibrate. The target frequency typically is one of: theresonant frequency for the vibrational mode; the anti-resonant frequencyfor the vibrational mode; or a frequency between the resonant andanti-resonant frequencies. Since the resonant frequencies of thevibrational modes of the tip are different from each other, the targetfrequencies of the vibration modes are likewise understood to bedifferent.

In many versions of the invention, the potential of each component ofthe drive signal is at a potential designed to foster the flow of atarget equivalent of current through what are known as the mechanicalcomponents of the handpiece 32 and tip 142. These components includedrivers 36, post 44, proximal end mass 46 horn 48 and tip 152. Sleeve170 is typically not considered a component to which the equivalent ofcurrent flows. This is because, while the sleeve 170 vibrates, thevibration of the sleeve is due to the vibration of the other components.For simplification of further description, this will be further referredto simply as the equivalent of current through the mechanical componentsof the handpiece. This phrase will be used even though shell 170 can beconsidered a mechanical component of the handpiece 32.

FIG. 9A is a schematic representation of how the drive signal currenti_(S) is broken down into two components. The first component is currenti_(O), the current through the handpiece drivers 36. The secondcomponent is current i_(M), the equivalent of current through themechanical components of the handpiece. According to Ohm's law thecurrent through the drivers and the equivalent of current through themechanical components of the handpiece are function of the drive signalvoltage V_(S), and the impedance of these components. In FIG. 9A, Z_(O)is the impedance of the handpiece drivers 36. Impedance Z_(M) is theequivalent of reactance of the mechanical components of the handpiece.

The impedance of the drivers 36 is due primarily to their capacitivereactance. Accordingly, in the schematic diagram of FIG. 9B, the driverimpedance Z_(O) is depicted as being solely a function of drivercapacitance C_(O). For the purposes of system 30 of this invention,driver capacitance C_(O) is generally constant. The equivalence ofimpedance of the mechanical components of the handpiece has a resistivecomponent, an inductive reactance component and a resistive component.Accordingly, in FIG. 9B the equivalent of mechanical impedance Z_(M) isdepicted as being a function of a resistance R_(M), a capacitance C_(M)and an inductance L_(M). In FIG. 9B the mechanical equivalents ofresistance R_(M), capacitance C_(M) and inductance L_(M) are shown asvariable. This is because these characteristics of handpiece vary as afunction of the mechanical resistance to which the tip 142 is exposedwhen the tip is applied against tissue.

The equivalent of current that, at any one moment, flows through themechanical components of the handpiece is determined based on thefollowing equation:

i _(M) =i _(S) −jωC _(O) V _(S)  (1)

Here ω is the radial frequency of the drive signal. A detailedexplanation of how Equation (1) is derived can be found in theApplicant's U.S. Prov. Pat. App. No. 61/863,152 filed 7 Aug. 2103,SYSTEM AND METHOD FOR DRIVING AN ULTRASONIC HANDPIECE AS A FUNCTION OFTHE MECHANICAL IMPEDANCE OF THE HANDPIECE, the contents of which arepublished in the Applicant's also incorporated by reference PCT App. No.PCT/US2014/050034 published as WO 2015/021216 A1/U.S. patent Pub. Ser.No. ______. Both of the above-listed applications are explicitlyincorporated by reference into this application. As mentioned above, thedrive signal supplied by system 30 of this invention has pluralcomponents. The equivalent of current through the mechanical componentsof the handpiece for an individual component of the drive signal istherefore based on the following equation:

i _(M-X) =i _(S-X) −jω _(X) C _(O) V _(S-X)  (1A)

The “−X” or “X” identifies the particular component of the drive signalfor which the equivalent of current is being calculated.

As discussed above, system 30 of this invention is further configured tocontrol the drive signal so that each component of the drive signal isat a frequency that, as closely as possible, tracks a target frequencyof the mechanical components of the handpiece.

Generally, the relationship of the frequency of the drive signal to atarget frequency can be determined by first determining the realcomponent of the ratio of the current through the handpiece drivers 36to the equivalent of current through the mechanical components of thehandpiece. This ratio is expressed by the following Equation:

$\begin{matrix}{{- {Re}}\mspace{14mu} \left\{ \frac{j\; \omega \; V_{s}C_{O}}{i_{s} - {j\; \omega \; V_{s}C_{O}}} \right\}} & (2)\end{matrix}$

The incorporated by reference U.S. Prov. Pat. No. 61/863,152 provides adetailed explanation of why the above ratio provides the relationship ofthe frequency of the drive signal to a target frequency of themechanical components of the handpiece.

Since the drive signal applied to the handpiece drivers according tothis invention is made up of plural components, the ratio for a singlecomponent is:

$\begin{matrix}{{- {Re}}\mspace{14mu} \left\{ \frac{j\; {\omega \;}_{X}V_{S - X}C_{O}}{i_{S - X} - {j\; {\omega \;}_{X}V_{S - X}C_{O}}} \right\}} & \left( {2A} \right)\end{matrix}$

This ratio is compared to a constant target ratio (TR). The target ratiois typically a number between zero and one, inclusive. If it is theobjective that the component of the drive signal be at the resonantfrequency of the vibrational mode, the target ratio is zero. If it isthe object that the component of the drive signal be at theanti-resonant frequency of the vibrational mode, the target ratio isone. In an implementation of this invention wherein the target frequencyof the component of the drive signal be at a frequency between theresonant and anti-resonant frequencies of the vibrational mode the drivefrequency is a fraction between zero and one.

There may be situations when, comparing the ratio of Equation (2A) to atarget ratio, does not, by itself, provide a good indication of therelationship of the frequency of the drive signal component to thedesired target frequency. This can occur as a result of the placement ofthe tip head 158 against tissue. More particularly, an inherent featureof some tip heads is that when they are placed against tissue andsubjected to loading there are large variations in the equivalent ofreactance of the mechanical components of the handpiece over the rangeof frequencies that includes the target frequency. Further, sometimes apractitioner may want to position the tip head 158 against tissue beforeactuating the handpiece 32. When this occurs, the resistive component ofthe equivalent of impedance of the mechanical components of thehandpiece may be appreciably greater than both the capacitive reactanceand the inductive reactance of this components of this impedance. Ineither of these situations, the below discussed step of modifying thefrequency of the drive signal component so the ratio of Equation (2A) iscloser to the target ratio may not result the sourcing of drive signalthat has a component at a frequency close to the target frequency.

Accordingly, the below modified version of Equation (2A) is used todetermine if the component of the drive signal is at a frequency that isclose to the target frequency for the vibratory mode with which thecomponent is associated:

$\begin{matrix}{{{{- {Re}}\mspace{14mu} \left\{ \frac{j\; {\omega \;}_{X}V_{S - X}C_{O}}{i_{S - X} - {j\; {\omega \;}_{X}V_{S - X}C_{O}}} \right\}} + {m_{X}\left( {\omega_{X} - \omega_{{TRGT} - X}} \right)}^{A}} \approx {T\; F}} & \left( {2B} \right)\end{matrix}$

The portion of Equation (2B) on the right side of the plus sign modifiesthe basic ratio as a function of the difference between the actualfrequency of the component of the drive signal, ω_(X), and ω_(TRGT-X),the desired target frequency for the component of the drive signal.Exponent A is present because the modification may be based on a higherthan first order difference between the two frequencies. Coefficientm_(X) is the coefficient that defines the slope for defining themodification of the ratio as a function of the difference between theactual and target frequencies.

III. Actual Operation

Operation of system 30 of this invention starts with the coupling of thetip 142 to the handpiece 32. Sleeve 170 is fitted over the tip and alsoattached to the handpiece. 32. Cable 230 is attached to the controlconsole 240. Console 240 is then ready to be turned on. The abovesub-steps form the initial assembly and activation of the system, step302 in FIG. 10A. When the control console 240 is initially turned on,processor 276 reads the data stored in handpiece memory 56 and tipmemory 184, step 304. The processor 276 receives these data by assertingthe appropriate commands to the memory reader 272.

Based on the read data, in a step 306, processor completes the initialconfiguration of the system. Step 306 includes the performance of anumber of evaluations to determine whether or not the system 30 isproperly configured for use. These evaluations include: determining ifthe handpiece is one to which the control console 240 can supply a drivesignal; and determining if tip 142 is one that is appropriate foractuation by the handpiece. These evaluations may be based on data fromthe handpiece identification field 62 and from the tip identificationfield 188. Processor 276 also evaluates whether or not the handpiece 32and tip 142 are in conditions for use based on the read data from thehandpiece use history field 78 and the tip use history field 218. Anexample of data indicating that use may be inappropriate are dataindicating that a particular component, the handpiece or tip, has beenused for a number of times or an overall time that exceeds the designedlife cycle for the component.

Assuming the components are properly assembled for use as a system,processor 276 presents information to this effect on display 278.Processor 276 also invites the practitioner to enter informationindicating how system should be configured to ensure that the vibratorymovement of the tip head 158 is the movement desired by thepractitioner. The above are all part of step 306. The receipt of thepractitioner's initial configuration commands is also part of step 306.

Based on the data in the handpiece memory 56, the tip memory 184 and thepractitioner entered commands, processor 276 in a step 308, establishesa selected maximum equivalent of current, i_(SELECTMAX-X), through themechanical components of the handpiece for each of the components of thedrive signal. The present example of operation of the system is based onthe tip 142 of FIG. 3. Specifically, this tip 142 is designed so thatthe drive signal induces movement of tip head 158 in two planes,longitudinal and flexural. Accordingly, the drive signal is formed fromtwo components: a first component based on a target frequency associatedwith longitudinal plane vibration; and a second component based on atarget frequency associated with the vibration in the torsional plane.In step 308 the selected maximum equivalent of current is establishedfor each of the components of the drive signal using the followingequation:

i _(SELECTMAX-X) =B _(X) i _(M) ^(MAX-X)  (3)

The select maximum equivalent current i_(X) ^(SELECTMAX-X) is understoodto be based on the practitioner's setting regarding the path of travelof the tip. Coefficient B_(X) is the coefficient processor 276 generatesbased on the practitioner's setting. Accordingly, a first part of theexecution of step 308 is for the processor 276 to, based on thepractitioner's settings, generate the appropriate B_(X) coefficients.Coefficients B_(X) may be generated based on reference to a look-uptable. Alternatively, the B_(X) coefficients are based on algorithms notpart of this invention. These algorithms, based on the informationregarding the practitioner-set path of travel, output B_(X) coefficientsthat result in the generation of i_(X) ^(SELECTMAX) equivalent that whendefining the drive signal result a drive signal being applied to thehandpiece that causes the tip head to move in the desired path oftravel.

In the described version of the invention, the drive signal has twocomponents. Accordingly, in step 308 Equation (3) is executed twice. Thefirst time the equation is executed the maximum equivalent current forthe first drive signal component, the equivalent of current i_(M)^(MAX1) from maximum current field 192 is employed as variablei^(MAX-X). The second time Equation (3) is executed the equivalent ofcurrent, current i_(M) ^(MAX2), from field 194 is employed as variablei_(M) ^(MAX-X). Once the select maximum equivalents of current aregenerated, system 30 is ready for actuation.

Step 310 represents the processor waiting to determine if the controlmember has been actuated to indicate the practitioner wants to activatethe handpiece, vibrate the tip head 158. In the described embodiment ofthe invention, processor 276 executes step 310 by monitoring the signaloutput by footswitch 280. When the practitioner wants to actuate the tiphe/she depresses the footswitch 280. The magnitude of tip headvibrations is set by the practitioner controlling the extent to whichthe footswitch 280 is depressed.

Upon the processor 276 receiving signals from the footswitch indicatingthe switch has been depressed the processor executes step 312. In step312 the processor 272 establishes a target equivalent of current foreach of the components of the drive signal, i_(M) ^(TARGET1) and i_(M)^(TARGET2). In many versions of the invention, each target equivalent ofcurrent is calculated using a first order equation:

i _(M) ^(TARGET-X) =Di ^(SELECTMAX-X)  (4)

Coefficient D is between 0.0 and 1.0, inclusive. If, for example, thepractitioner wants the tip head to undergo vibrations of maximumamplitude, the footswitch 280 is typically fully depressed. Processor276, in response to receiving signals indicating that the footswitch 280is in this state, sets coefficient D to unity. If the practitioner wantsthe tip head 158 to have vibrations at less than the maximum amplitudethe practitioner does not fully depress the footswitch 280. Processor276 upon receiving a signal that the footswitch 280 is only partiallydepressed sets coefficient D to a value between zero and unity as afunction of the extent to which the switch is depressed.

When console 240 initially executes the control loop of FIG. 10A-10D,the first execution of the loop after the evaluation of step 310 testspositive, the processor 276 executes a step 314. In step 314 the initialcharacteristics of the components of the drive signal are generated. Thefrequency of each component is referred to as variable FREQ_COMP-X. Thevoltage of each component is referred to as variable VOLTAGE_COMP-X.Each component of the drive signal has an initial frequency and aninitial potential. The initial frequency for a component is the minimumfrequency for the component as read from the tip memory 158. For thefirst component, this is the frequency contained in memory field 196.For the second component, this is the frequency contained in memoryfield 206. The initial potential is a potential that is a fraction ofthe maximum potential for that component of the drive signal. In someversions of the invention, the initial potential is between 0.03 and0.07 of the maximum potential, V_(S) ^(MAX-X) for that component of thedrive signal. For the first component of the drive signal the potentialfrom tip memory field 191 is employed as V_(S) ^(MAX-X). The potentialfrom tip memory field 193 functions as V_(S) ^(MAX-X) for thecalculation of the initial potential for the second component of drivesignal.

Based on the characteristics of the individual components of the drivesignal, control console 240, in a step 315, then outputs the drivesignal. As part of step 315, the processor 276 generates a waveform thatrepresents the sum of the two components of the drive signal. Thiswaveform has the appearance of the waveform of FIG. 8. The processor 276that generates a WAVEFORM_SET signals that represent this waveform. TheWAVEFORM_SET signals are then applied to the input of the amplifier 244to which the gain control signal is supplied.

Amplifier 244, in response to receipt of the WAVEFORM_SET signal, and aspart of step 315, selectively amplifies and attenuates the signal fromthe power supply 242. The output signal from the amplifier is applied tothe transformer primary winding 254. Transformer 248 outputs the drivesignal over cable 230 to the handpiece drivers 36. The above are allpart of step 315.

In response to the application of the drive signals to the handpiecedrivers 36, the drivers cyclically expand and contract. Theexpansion/contraction of the drivers is proportional to the potential ofthe drive signal. The expansions/contractions are proportion to theamplitude of the drive signal and at the frequency of the drive signal.Handpiece horn 48 amplifies and transfers these expansions andcontractions to proximal section 146. These vibrations are along thelongitudinal plane of the tip. Grooves 152 convert a fraction of thisshaft movement into vibrations in the torsional plane. Owing to thevarying potential of these vibrations and the structure of the tip, thetip head 158 is induced into a vibratory movement that, as depicted inFIG. 11 is non-linear. In FIG. 11, immediately to right of the leftmostequals sign, the movement as seen as the single elliptical path oftravel.

In this invention, since the components of the drive signal do not havethe same frequency, that paths of travel of two consecutive vibratorycycles will not be identical. This results in the tip head undergoingvibrations that in addition to not being linear, change orientationsover time. The single elliptical loop of FIG. 11 should actually not bea closed loop. In FIG. 11, the middle plot to the right of themiddle-located equals sign shows the path of travel of a point on thetip head after the tip head is engaged in plural vibratory cycles. InFIG. 11 the plot furthest to the right of the equals sign shows the pathof the travel of the tip head point after the tip head is engaged isstill more vibratory cycles. These plots indicate that, over a period oftime the point on the tip head, the point on the tooth will subtend asurface. While the surface in FIG. 11 natural appears curved, it shouldbe understood that the surface may curve around one or more axes.Implicit in this movement of the tip head point is that, in consecutivevibratory cycles, the orientation of a path of travel of the pointchanges.

System 30 engages in a feedback control process to ensure that theoutput drive signal continues to induce the desired movement of the tiphead 158. To perform this control, in step 154, processor 272, in step316 monitors the system 96 monitors the voltage V_(S) of the drivesignal through the handpiece. This is the monitoring by the processor272 of the output signal produced by voltage measuring circuit 262. Aspart of this monitoring, processor breaks down the voltage V_(S) intoplural components. Specifically, the voltage V_(S) is broken down intoone component for each component that comprises the drive signal. In thedescribed version of the invention the drive signal has two components.Therefore voltage V_(S) is broken down into a first component potential12 and a second component potential v_(S) ². In some versions of theinvention, processor 272 employs a Fast Fourier Transformation to sobreak down the components of voltage V_(S).

As part of the feedback control, in step 318, the processor 272 monitorsthe drive signal current through the handpiece, current i_(s). Thismonitoring is performed with the current measuring circuit 266. As withdrive signal potential, drive signal current is made of a pluralcomponents, one component for each component of the drive signalAccordingly, as part of step 318, the processor breaks down the drivesignal current into a first component characteristic current i_(S) ¹ anda second component characteristic current i_(S) ². In step 318,processor 272 performs a Fast Fourier Transformation to perform thisbreak down the measured handpiece current i_(S) into i_(s) ¹ and i_(S)².

In a step 320, processor determines the equivalent of current for eachcomponent of the drive signal. As this equivalent of current iscalculated, not measured, it is sometimes referred to as the calculatedequivalent of current. In step 320 Equation (1A) is employed todetermine i_(M) ^(CALC1), the calculated equivalent of current for thefirst component of the drive signal and i_(M) ^(CALC2), the calculatedequivalent of current for the second component of the drive signal.

The variables used to determine the calculated currents i_(M) ^(CALC1)and i_(M) ^(CALC2) include the respective potentials Vs and V_(S) ² forthe individual components of the drive signal potentials. The abovecalculated first and second components current characterisitics, i_(S) ¹and i_(S) ² are also input variables into the determination ofcalculated equivalents of current that occurs in step 320. A thirdvariable in each determination of calculated equivalent of current isthe frequency characteristic of the component of the drive signal. Forthe first component of the drive signal this is ω₁, for the secondcomponent this is ω₂. In step 320 the frequency the frequencycharacteristics of the previously generated first and second componentsof the drive signal are employed as these variables. This means that inat least the preferred version of the invention, measured or calculatedrepresentations of the frequency characteristics are not employed asfeedback data to regulate the outputting of the drive signal.

Equation (1A) has an additional variable, capacitance C_(O) of thehandpiece drivers 36. Processor 272 employs the driver capacitance readfrom handpiece memory field 64 as this capacitance.

In a step 322 the calculated equivalent of current for the firstcomponent of the drive signal is compared to the target equivalent ofcurrent for this component of the drive signal. This comparison isperformed because if the equivalent of current is below the targetequivalent of current, there is a significantly likelihood that thevibrations in the associated vibratory mode are not of sufficientamplitude to foster the desired movement of the tip head 158. If theequivalent of current to which the mechanical components of thehandpiece are exposed is greater than target equivalent of current, thetip head 158 may be undergoing vibrations of an amplitude greater thanthat desired by the practitioner.

In some versions of the invention, the equivalent of current applied tothe mechanical portions of the handpiece is fostering the desiredvibrational movement if the calculated equivalent of current is within10% or less of the target current. Alternatively, the current is ofsufficient magnitude if the two currents are within 5% or less of eachand ideally, within 1% or less of each other.

If the two equivalents of current are substantially equal, system 30 isin the state in which the equivalent of current flow through themechanical components of the handpiece is at level at which theapplication of the drive signal assuming at the correct frequency,inducing vibrations of appropriate amplitude in tip head 52 in theassociated vibratory mode. If system 30 is in this state, processor 96proceeds to step 326.

In many situations, the comparison of step 322 indicates that calculatedmechanics equivalent of current i_(M) ^(CALC1) is not substantiallyequal to target current i_(M) ^(TARGET1). When system 30 is in thisstate, processor 272 in a step 324 resets the potential characteristicof the first component of the drive signal. More specifically, theprocessor 272 calculates a value for potential VOLTAGE-COMP1, thatwould, based on Equation (3), result in an adjusted current flow throughthe mechanical components of the handpiece that substantially equal totarget equivalent of current i_(M) ^(TARGET1). This calculation of step324 is executed based on driver capacitance and frequency characteristicof the drive signal remaining constant.

In step 326 processor 272 determines if the frequency characteristic ofthe first component of the drive signal is at or substantially equal tothe target frequency for this component of the drive signal. Thisdetermination is made to ensure that the frequency characteristic of thefirst component is resulting in the outputting of drive signal thatfosters the desired movement of the tip head. In step 326 thisdetermination is made by comparing the ratio of Equation (2B) to thetarget ratio. The variables used in step 318 to produce the calculatedequivalent of current are used to produce this ratio. The remainingvariable used to produce this ratio is the target for the frequencycomponent. This is the ω_(TARGET1) variable from filed 202 of the tipmemory 184. Coefficient m₁ is from coefficient field 204 of the tipmemory 184. The exponent A is assumed constant and identical for allcalculations generating the ratio modifier. It is within the scope ofthis invention that exponent A can vary.

The frequency characteristic is sometimes considered substantially equalto the target frequency characteristic if the ratio is within 10% of thetarget ratio. In still other versions of the invention, the frequenciesare considered substantially equal of the ratio is within 5% of thetarget ratio and more preferably within 1% of the target ratio.

The comparison of step 326 may indicate that the frequencycharacteristic of first component of the drive signal is at orsubstantially equal to the target frequency for this component of thedrive signal. This means that drive signal is inducingexpansions/contractions of the drivers 40 that result in movement of thetip head at the desired pattern. If system 30 is in this state,processor 272 proceeds to execute step 330.

It may be determined in the evaluation of step 326 that the frequencycharacteristic of the first component of the drive signal is resultingin the output of a drive signal that does not induce the desired patternon tip head movement. If processor 272 makes this determination, in astep 328 the processor adjusts the frequency characteristic, FREQ-COMP1,of this component of the drive signal. Owing to the ratio on the leftside of Equation (2B) being negative, the calculation of step 164yielding a negative result is, in 328 interpreted as an indication bythe processor 272 that the frequency characteristic of the firstcomponent of the drive signal should be increased. If the calculation ofstep 326 yields a positive result, processor 272 interprets the resultas indicating the handpiece is in a state in which it is necessary todecrease the frequency characteristic of the first component to increasethe likelihood that the tip head is undergoing the desired path oftravel.

After the execution of step 326 or, if necessary step 328, processorexecutes step 330. Step 330 is a comparison of the calculated equivalentof current for the second component of the drive signal to the targetfor this equivalent of current. Step 330 is substantially the same asstep 322. The difference between steps 322 and 330 is that in step 330calculated i_(M) ^(CALC2) is compared to target current i_(M)^(TARGET2). Assuming the two values are substantially equal the voltagecharacteristic of the second component of the drive signal is notadjusted. Processor executes a step 334.

If the two values compared in step 330 are not substantially equal, in astep 332, the processor resets the voltage characteristic of the secondcomponent of the drive signal. The means by which step 332 issubstantially the same as the means in employed in step 324 to reset thevoltage characteristic of the first component of the drive signal. Aspart of step 332 processor 272 resets the WAVEFORM_SET signal based onany resetting of the voltage characteristic of the second component ofthe drive signal. The characteristics of the drive form likewise change.

After step 330 and if, necessary, step 332, is executed, in a step 334,the frequency characteristic of the second component of the drive signalis evaluated. This evaluation is performed using the same process usedin step 326 to evaluate the frequency characteristic of the firstcomponent of the drive signal. In step 334 the variables of secondcomponent of the drive signal are applied to Equation (2B). In this useof Equation (2B), the target frequency ω_(TARGET2) is from tip memoryfield 210 is used in the modifying component of the ratio to determineif the second component of the drive signal has an appropriate frequencycharacteristic. Coefficient m₂ from tip memory field 208 is used as thecoefficient of the modifying component of the ratio. The evaluation ofstep 334 may indicate that the frequency characteristic of the secondcomponent of the drive signal is sufficiently equal to the targetfrequency. When system 30 is in this state, the processor loops back tostep 310 to determine if the control member remains activated.

Alternatively, the evaluation of step 334 may indicate that frequencycharacteristic of the second component of the drive signal is notsubstantially equal to the target frequency. If system 30 is in thisstate, processor 276, in a step 336 resets this frequencycharacteristic.

Upon the execution of step 336, the processor loops back to step 310. Ifthe evaluation of step 310 during this execution of the step indicatesthe on/off switch remains actuated, step 312 is reexecuted. This stepreexecuted because the practitioner may have entered commands indicatedthat the magnitude of the vibrations are to be reset from the previoussetting.

Since the frequency and voltage characteristics of the components of thedrive signal have been previously set, in this execution of the controlloop, step 314 is not executed. Instead, based on the previouslygenerated set of the drive signal component characteristics, step 315 isreexecuted. If the characteristics of the drive signal components havechanged since the previous execution of step 315, this will result inprocessor 276 generating a new WAVEFORM_SET signal. The control consolewill then in turn output a new drive signal the characteristics of whichhave been adjusted based on the previously calculated adjustments to thecharacteristics of the individual components of the drive signal.

In the subsequent executions of the control loop it is understood thatthe reset frequency characteristics of the components of the drivesignal are employed as variables ω₁ and ω₂ to determine if the drivesignal is inducing the desired movement of the tip head 158.

Inevitably, there will be a time when the handpiece is to bedeactivated. The practitioner stops actuating the on/off switch. When itis determined in step 310 that this event has occurred, the processor276 asserts the command the result in the other components of theconsole 240 terminating the application of drive signal to the handpiece(steps not shown).

While not shown, it is also understood that both during the initialsetting and subsequent readjustments of the WAVEFORM_SET signal, theprocessor 272 ensures that the drive signal is limited by the boundarycharacteristics read from both the handpiece memory 56 and tip memory184. These limits include limiting: the voltage of the drive signalbased on the maximum drive signal voltage from handpiece memory field70; the voltage characteristic of the first component of the drivesignal based on the voltage data in tip memory field 191; the voltagecharacteristic of the second component of the drive signal based on thevoltage data in tip memory field 193; the maximum current of the drivesignal based on the data from the handpiece memory field 66; the maximumequivalent of current to the handpiece based on the data from handpiecememory field 68; the maximum equivalent of current for the firstcomponent of the drive signal based on the data from tip memory field192; and the maximum equivalent of current for the second component ofthe drive signal based on the data from tip memory field 194.

The frequency characteristics of the drive signal is likewise set basedon data read from the handpiece and tip memories 56 and 184,respectively. Thus, the data from handpiece memory fields 72 and 74 areused to define the overall boundaries of the drive signal. The frequencyrange data from tip memory fields 196 and 198 define the range offrequencies of the frequency characteristic of the first component ofthe drive signal. The frequency range data from tip memory fields 206and 208 define the range of frequencies of the frequency characteristicof the first component of the drive signal.

As mentioned above, system 30 of this invention is configured to vibratethe tip head 158 so that, in a single vibratory cycle, a point on thetip head does not simply reciprocate back and forth along a line.Instead, the point of engages in a non-linear path of travel. When atooth, the point of the tip head, moves against the bone, the toothstrikes the bone and immediately thereafter rubs against the bone. Thestriking of the bone fractures the bone to foster the removal of tissue.The immediately following action of the tooth rubbing against the boneclears the just removed material away from the bone. There is thus ashort period of time between when system 30 of this invention removesbone and clears away the removed tissue. During the next vibratorycycle, only a relatively small amount of debris are present. Theminimization of these debris results in a like reduction in the extentto which the presence of these debris adversely affects the bone cuttingprocess.

When the system of this invention drives the tooth of a tip head innon-linear movement, during a single cycle, essentially the whole of thecircumference of the tooth is forced against the tissue against whichthe tip head is placed. This tooth-against-tissue movement is whatresults in the desired scraping away, the removal of, the tissue. Sinceduring a single cycle of movement essentially every surface of the toothis forced against the tissue, each surface is exposed to at least somewear. Thus, this invention reduces the extent to which the toothsurfaces are subjected to appreciably uneven wear. It is believed thatminimizing the uneven wear of the individual teeth results in a likereduction in the extent to which the cutting efficiency of the teeth arereduced. This reduces the likelihood that, in a procedure, the cuttingefficiency of the set of teeth of a tip will degrade to a level that itbecomes desirable, if not necessary, to replace the tip.

Moreover, since during a single cycle of movement, essentially eachsurface of the tooth is urged against tissue, there is no extendedperiod of time in the cycle during which a single surface of the toothis pressed against the tissue. This limits the frictional heating of atooth surface that could otherwise occur if that surface is socontinually pressed against tissue. The limiting of this heating reducesthe extent to which this heat, if allowed to develop, could damage thetissue surrounding the tissue adjacent the tip head.

It should be further understood that system 30 can vibrate a tip inplural vibrational modes that are of different frequencies. Tips can beused with this system that are not limited to tips that, when vibratingin two modes, vibrate at a common frequency. There are appreciablemanufacturing constraints and costs associated with have to provide atip that, when it vibrates at plural modes, does so at a commonfrequency. These constraints and costs are typically not associated withproviding a tip that, when it vibrates in plural modes, does so atdifferent frequencies. System 30 of this invention therefore makes itmore feasible both in terms of manufacturing and economics to providedifferent tips able to vibrate simultaneously in different modes.

A further feature of this invention is that the practitioner can set thepath of the non-linear travel of the tip head. More specifically, inresponse to the practitioner set definition of this path of travel,processor 276, in step 308, sets the individual maximum equivalents ofcurrent, the i^(SELECTMAX-X) current, for the individual vibrationalmodes. By setting one i^(SELECTMAX-X) current to be relatively large andthe second i^(SELECTMAX-X) current to be relatively small, the resultantdrive signal is one that will in a single cycle of tip head movementcause the tip to undergo a relatively large movement along the firstvibratory path and a smaller movement in the second vibratory path. Bysetting the i^(SELECTMAX-X) currents for the two vibrational modes to besubstantially equal, the drive signal will induce movement that canresult in the tip undergoing the simultaneous movement in the twodifferent vibratory paths that are more equal in displacement.

There are times a practitioner may want to apply the tip head to tissuethat is appreciably radially spaced from the longitudinal axis of thetip shaft. To perform a procedure on tissue so positioned it isdesirable to provide the tip with a head that is asymmetrically locatedrelative to the longitudinal axis of the tip shaft. Owing to thisasymmetry the tip head naturally vibrates in plural modes. Typically,these vibratory modes are at different frequencies. System 30 of thisinvention, by regulating the vibrations in these plural modes makes itpossible to ensure that when the tip head vibrates the movement is alonga path of travel that is both predictable and results in the efficientremoval of tissue.

Further since the tip head excited into vibration according to thisinvention moves in a non-linear pattern, each tooth tends to push thecut tissue away from the path of travel. This clearing of the tissueaway from the teeth reduces the extent to which these debris reduce theefficiency of tissue cutting in the following vibratory cycles.

The above is directed to one version of the system of this invention.Other versions of the system of this invention may have featuresdifferent from what has been described. For example, some tips of thissystem may have three or more vibratory modes. For this configuration ofthe system, the drive signal will have three or more components. Itshould be further understood that the target frequency characteristicsfor some of these components may be close to if not identical to eachother. Likewise there may be times when the equivalent of currentapplied to the mechanical components of the handpiece may be for thedifferent components of the drive signal substantially, if not exactly,identical.

The structure of the components of the system may vary from what hasbeen described. Thus, in some versions of the system, internal to theconsole there are plural signal generators that operate simultaneouslyand independently from each other. The processor regulates the voltageand frequency of the signals produced by each of these signalgenerators. More specifically, the processor controls each signalgenerator so that signal generator outputs a specific component of thedrive signal. These individual components are added together to producethe drive signal that is applied to the handpiece drivers 36.

In some versions of the invention the assembly that supplies the drivesignal to the handpiece may not include an amplifier that varies thevoltage applied to the console transformer. In these versions of theinvention, the assembly that supplies signal upon which the drive signalis based included a variable current source.

It should thus be appreciated that in alternative versions of theinvention, assemblies other than the disclosed coils 256 and 264 may beemployed to provide the measure of the potential of the drive signalacross the handpiece and the current through the handpiece. In someversions of the invention, one or more resistor networks may provide thesignals upon which these measures of voltage and current and determined.

There is no requirement that in all versions of the invention drivercapacitance be based on data read from a memory integral with thehandpiece. In alternative versions of the invention, the processor byoutputting drive signals at various frequencies and measuring thevoltage and current of the drive signals determines the capacitance ofthe drivers.

In some versions of the invention based on performing frequency sweepsthe processor determines the resonant and anti-resonant modes of each ofthe vibratory modes.

In some configurations of the invention, it should be understood thatwhile the path of travel of a point of the tip head 158 is non-linear,for all intents and purposes, the path appears as a linear path.

In FIG. 11 the illustrated non-linear path is seen as a path that areessentially elliptical. This is understood to be exemplary and notlimiting. Other single vibratory paths of this invention may have othershapes. These shapes include essentially circular and essentiallycrescent shaped. It is further within the scope of this invention thatthe non-linear path includes paths that cross over each other. Theclassic form of this type of path is the figure eight path.

In some versions of the invention the potential of one or more of thecomponents of the drive signal may be fixed. In these versions of theinvention the equivalent of current applied to the mechanical componentsof the handpiece is regulated by the adjustment of the target frequencyassociated with the component.

Further it should be understood that while generally the frequencycharacteristics of the components of the drive signal are different,this may not always be the case. There may be times when, based on thetype of mechanical load applied to the tip 158, the frequencycharacteristics of the two or more components of the drive signal may beidentical.

Accordingly, it is an object of the appended claims to cover allvariations and modifications that come within the true spirit and scopeof this invention

What is claimed is:
 1. An assembly for vibrating the tip of anultrasonic handpiece, the handpiece having at least one driver with acapacitance to which an AC drive signal is applied, the tip having ahead that is applied to a tissue to accomplish a surgical task, the tipbeing designed to vibrate in plural modes, the assembly including: anassembly for generating a variable AC drive signal that is applied tothe at least one driver of the handpiece; an assembly for measuring thevoltage of the drive signal applied across the handpiece that outputs asignal representative of drive signal voltage; an assembly for measuringthe current through the handpiece that outputs a signal representativeof current through the handpiece; and a processor that receives from thesignal representative of drive signal voltage, the signal representativeof current through the handpiece that and data describing thecapacitance of the at least one driver and that is configured to:breakdown the measured voltage of the drive signal into pluralcomponents, wherein each component of the measured voltage representsthe measured voltage associated with a specific vibratory mode of thetip; breakdown the measured current through the handpiece into pluralcomponents, wherein each component of the measured current representsthe measured current through the handpiece associated with a specificvibratory mode of the tip; for each vibratory mode of the tip” determinea target current, the target current being the equivalent of current tobe applied to the mechanical components of the handpiece; based on thevoltage of the drive signal, the current of the drive signal, thefrequency of the drive signal and the capacitance of the at least onedriver, calculating an equivalent of current applied to mechanicalcomponents of the handpiece; compare the target current to thecalculated equivalent of current applied to the mechanical components ofthe handpiece; based on the current comparison, set the potential of thedrive signal output by the assembly that generates the drive signalbased on the voltage of the drive signal, the current of the drivesignal, the frequency of the drive signal and the capacitance of thepiezoelectric driver, calculating a ratio between current applied to theat least one driver and the equivalent of current applied to themechanical components of the handpiece; and based on the calculatedratio, set the frequency of the drive signal output by the assembly thatgenerates the AC drive signal; and based on the voltage characteristicsand frequency characteristics of the plural vibratory modes, determinethe structure of the waveform of the drive signal and assert a commandto the assembly that generates the drive signal so as to cause theassembly to generate a drive signal that contains a component for eachvibratory mode, each component being defined by the voltagecharacteristic and frequency characteristic determined for thatvibratory mode.
 2. The assembly of claim 1, wherein said processor isfurther configured to determine the structure of the waveform of thedrive signal applied to the at least one driver of the handpiece sothat, as a result of the application of the drive signal, the head ofthe tip in a single vibratory cycle engages in a non-linear path oftravel.
 3. The assembly of claim 1, wherein said processor is furtherconfigured to: for each vibratory mode of the tip, establish an initialfrequency characteristic for the component of the drive signalassociated with the vibratory mode based on data stored in a memory. 4.The assembly of claim 3, wherein said processor is further configured toread from a memory associated with the tip the data used to establishthe initial frequency characteristics for the components of the drivesignal.
 5. The assembly of claim 1, wherein the processor is furtherconfigured to for each vibratory mode of the tip, establish an initialvoltage characteristic for the component of the drive signal associatedwith the vibratory mode based on data stored in a memory.
 6. Theassembly of claim 5, wherein said processor is further configured toread from a memory associated with the tip the data used to establishthe initial voltage characteristic for the components of the drivesignal.
 7. The assembly of claim 1, wherein said processor is furtherconfigured to, for at least one vibratory mode of the tip, determine thetarget equivalent of current through the mechanical components of thehandpiece based on a practitioner set command.
 8. The assembly of claim1, wherein said processor is further configured to for plural vibratorymodes of the tip, determine the target equivalents of current throughthe mechanical components of the that handpiece based on a practitionerset command.
 9. The assembly of claim 1, wherein said processor isfurther configured to determine the structure of the waveform of thedrive signal applied to the at least one driver so that, as a result ofthe application of the drive signal, the head of the tip in a singlevibratory cycle travels in a loop.
 10. The assembly of claim 1, wherein:said assembly for generating the drive signal includes a variable gainamplifier; and said processor regulates the gain of the signal producedby said amplifier so that said amplifier outputs a signal that has thefrequency of the drive signal and that is at least proportional to thepotential of the drive signal.
 11. The assembly of claim 1, wherein: theassembly for generating the drive signal includes a transformer having aprimary winding to which a signal proportional to the drive signal isapplied and a secondary winding across which the drive signal isdeveloped; and the assembly for measuring the voltage of the drivesignal includes a tickler coil integral with said transformer acrosswhich the signal present across the secondary winding induces a signal.12. The assembly of claim 1, wherein said assembly for measuring currentthrough the handpiece includes a coil adjacent a conductor across whichthe drive signal is applied to the handpiece, said coil being positionedso that the drive signal induces a signal across said coil.
 13. Theassembly of claim 1, wherein said processor is configured to determinethe current through the at least one driver as function of thecapacitance of the at least one driver and the voltage and frequency ofthe drive signal.
 14. The assembly of claim 1, wherein said processor isconfigured to: determine if the calculated ratio between current appliedto the at least one driver and the equivalent of current applied to themechanical components of the handpiece indicates that the drivefrequency is substantially equal to a target ratio, the target ratiobeing based on a target frequency for the vibrations of the mechanicalcomponents of the handpiece; and if the determination indicates thecalculated ratio is not substantially equal to the target ratio, adjustthe frequency of drive signal.
 15. The assembly of claim 14, wherein thetarget frequency for the vibrations for of the mechanical components ofthe handpiece for at least one of the vibratory modes is one of: theresonant frequency of the vibrations of the mechanical components of thehandpiece; the anti-resonant frequency of the vibrations of themechanical components of the handpiece; or a frequency between theresonant and anti-resonant frequency of the vibrations of the mechanicalcomponents of the handpiece.
 16. The assembly of claim 1, wherein saidprocessor is further configured to: obtain from a memory associated withthe handpiece data representative of the capacitance of the at least onedriver; and at least upon initial activation of said system: calculatethe equivalent of current applied to mechanical components of thehandpiece based on the driver capacitance data obtained from thehandpiece memory; and calculate the ratio between current applied to thepiezoelectric driver and the equivalent of current applied to themechanical components of the handpiece based on the driver capacitancedata read from the handpiece memory.
 17. The assembly of claim 1,wherein said processor, by setting the frequency and voltage of thedrive signal is configured to determine the capacitance of the at leastone driver of the handpiece.